Drag reduction article

ABSTRACT

A conformable drag reduction article is provided having a patterned surface capable of reducing drag resistance by fluid flowing thereover.

This is a continuation off application Ser. No. 07/517,757, filed May 2,1990now U.S. Pat. No. 5,069,403, which is a continuation of applicationSer. No. 06/740,239, filed May 31, 1985, now U.S. Pat. No. 4,986,496.

TECHNICAL FIELD

This invention relates to the reduction of drag caused by fluids (e.g.,air, gas, water, etc.) flowing across surfaces. More particularly itrelates to articles which can be applied to surfaces to reduce suchdrag.

BACKGROUND ART

It has long been a desire to reduce drag caused by the passage of bodiesthrough fluid media. Relatively small reductions in drag cansignificantly reduce the fuel needed to propel a body. For example, ithas been estimated that a one percent reduction in drag across theleading edge of a wing of a Boeing 727 airliner could reduce fuelconsumption by more than 20,000 gallons per airplane per year. SeeAutomotive Engineering, Feb., 1982, pp. 73.

The reduction of drag across surfaces of a body also is of benefit inother applications. By way of example, it is desirable to reduce thedrag caused by water flowing past the hull of a boat, air flowing past amoving automobile or air flowing past the blades of a windmill fan,airfoil, fan, rotor, stator, inlet, etc. Many other examples are ofcourse known as will be appreciated by those in the art. However, as yetthere has not been provided a practical solution to the problem ofreducing drag.

Many techniques have been proposed which involve mechanically alteringflow control surfaces. For example, the utilization of various devicesto direct air into ducts that exit at the trailing edges of the flowcontrol surface has been suggested. See, for example, U.S. Pat. Nos.2,742,247; 2,925,231; 3,117,751; 3,521,837; 4,114,836; 4,258,889; and4,296,899.

U.S. Pat. No. 4,434,957 suggests the use of a corrugated controlsurface. The corrugations that extend transversely to the direction ofthe fluid flow, temporarily retain vortices formed in the fluid flow onthe flow control surface, and aid in regulating their passage across thesurface.

U.S. Pat. No. 4,455,045 proposes the use of one or more 3-sidedsubmerged channels in the flow control surface. Each channel includestwo divergent walls which form a generally V-shaped ramp which is slopeddownward so that the channel widens and deepens toward the downstreamflow of the fluid. Such channels are V-shaped in a plane generallyparallel to the flow control surface. They are intricate and are mosteffective when provided in a serial cascade wherein the last channel inthe cascade ends at the trailing edge of the flow control surface.

These techniques are expensive, time consuming to employ and do notaddress the problem of how to reduce drag across the surfaces ofexisting equipment (e.g., airplanes, automobiles, etc.) in a practicalway.

The use of smooth surface coatings on airplane skins has also beensuggested. See Automotive Engineering, Feb., 1982, pp. 73-78. However,this article reported that liquid polymeric coatings and adhesivelybacked films, applied to the flow control surfaces in order to maintaina smooth, protected surface for drag reduction, performed poorly andwere unsuitable for areas of high erosion such as wing and tail leadingedges and nacelle inlets.

DISCLOSURE OF THE INVENTION

The present invention provides a practical technique for significantlyreducing drag across flow control surfaces. The invention comprises aconformable sheet material which employs a patterned first surface tosignificantly reduce drag caused by fluid flowing over the surface of abody to which the sheet has been applied. As used herein, conformablemeans that the article assumes the shape of the surface to which it isapplied without cracking or breaking and without the formation of anyair bubbles or wrinkles. Additionally, it does not release from thesurface even when it is under extreme stress, such as elongation andcompression, once it has been applied. For example, the article of theinvention will conform exactly to curved surfaces and riveted surfacessuch as are encountered on the skin of an airplane.

In a preferred embodiment of the invention, the article is capable ofwithstanding extended exposure to water, oil, hydraulic fluids and thelike without noticeable deterioration in its physical properties orappearance.

The article of the invention is convenient to use and provides a simpleyet versatile technique for reducing drag across flow control surfaces.It can be applied to the flow control surfaces of existing equipment orit can be applied to flow control surfaces of new equipment at the timeof manufacture. In either case the reduction in drag across the surfaceof such equipment is virtually identical.

The reduction of drag achieved by the article of the invention variessomewhat depending upon the body to which it is applied and theconditions at which the body operates. However, reductions in drag of upto 10% or more can be achieved with the present invention.

The present invention also provides a method for reducing drag caused byfluid flowing across flow control surfaces. The method includes thesteps of positioning the article over the body so that the patternedsurface will contact the fluid and provide maximum drag reduction;conforming the article to the shape of the body; and attaching thearticle to the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of the invention.

FIGS. 2 and 3 are cross sectional views of two alternative embodimentsof the invention.

FIGS. 4-8 represent greatly enlarged cross sectional views ofalternative patterned surfaces useful in the invention.

FIG. 9 represents a cross sectional view of the article of the inventionbearing graphic indicia.

DETAILED DESCRIPTION

The article of the invention may be characterized by a number of tests.For example, the article preferably has a tensile strength of greaterthan 200 kg/cm² measured according to ASTM D 2370. The conformability ofthe article may be demonstrated by subjecting the article to flexibilitytests MIL-P-38477A and MIL-M-437l9B. Specifically, the article will showno change after being subjected to the following tests (a) folding thearticle 20 times at room temperature (e.g., 20° C.); (b) dropping a 2.3kg steel ball onto the article from a height of 3 meters at atemperature of -29° C.; and (c) bending the article around a 2.5 cmmandrel at temperatures of from -54° C. to 121°C.

Preferred embodiments also exhibit resistance to a number of solvents.Thus, when tested according to MIL-M-437l9B the preferred embodimentshows no change after one hour in jet fuel. When tested according toMIL-P-38477A the preferred embodiment shows no change after either 2hours at 107° C. in hot oil or 240 hours in salt spray. When testedaccording to BMS-10-30A, the preferred embodiment of the invention willshow no change after 72 hours in TT-S-735 hydrocarbon fluid.Additionally, the preferred embodiment will show less than 0.15 cm edgelift after 72 hours in MIL-L-7808 lubricating oil and less than 0.3 cmedge lift after 24 hours in BMS-3-11.

The article of the invention is typically a film (i.e., it has width tothickness ratio of at least 5:1). Generally it is from 50 to 650 micronsthick. Preferably it is from 75 to 160 microns thick when used in highspeed applications (e.g., aircraft) and from 150 to 500 microns thickwhen used in low speed applications (e.g., automobiles). Preferably thefilms have a weight of less than 300 g/m² and most preferably a weightof less than 150 g/m².

Within these guidelines, a number of materials can be utilized toprovide the article of the invention. Useful materials includepolyolefins (e.g., polyethylene, unoriented polypropylene,ethylene/vinyl acetate polymers, ethylene/ethyl acrylate polymers),vinyl polymers (e.g., polyvinyl chloride, vinyl chloride/vinyl acetatepolymers, vinyl chloride/vinyl alcohol polymers, polyvinylidenechloride), polyurethanes (e.g., polyester and polyether urethanes),cellulosic films (e.g. cellulose acetate), and polyamide films (e.g.,nylon).

Other materials which may be employed to provide the article areradiation curable materials which generally comprise a radiation curablemonomer or prepolymer and an initiator. The monomer or prepolymergenerally contains at least two groups capable of reacting to form apolymer. A variety of such materials are known and include materialshaving functional ethylenically unsaturated groups (e.g., vinyl groups,acrylate and methacrylate groups, etc.).

Plasticizers, extenders, antioxidants, ultraviolet light stabilizers andthe like may be utilized in the article of the invention. Plasticizers(sometimes referred to as flexibilizers) are particularly helpful whenthe material used must be modified in order to meet the flexibilityrequirements of the invention. Materials useful for these purposes areknown. Typically they each comprise up to 5 parts by weight of thearticle.

While the exact material used to provide the article of the invention isnot critical, it is noted that certain materials will be better suitedto some applications than others. For example, thermoset flexiblematerials will be better suited than thermoplastic materials in thoseuses where high temperatures will be encountered. Water-resistant (e.g.,hydrolytically inert) materials will be better suited to use in waterenvironments than water-sensitive materials.

The article of the invention may be inherently adhesive, that is it neednot have a separate layer of adhesive applied to it. Such articles maybe either passively adhesive or actively adhesive. In the former casethe adhesive may be activated by solvents, heat, pressure, or the likeprior to application of the article to a substrate. In the latter case,such activation would not be necessary.

In the event that a separate layer of adhesive is employed, it is notedthat the adhesive may be selected from a wide variety of materials suchas heat activated adhesives, solvent (organic or inorganic) activatedadhesives, or pressure sensitive adhesives. These adhesives preferablyare compatible with the carrier to which they are applied and areresistant to water, oil, hydraulic fluids and the like. Furthermore, theseparate adhesive layer preferably does not separate from the carrierduring use.

Pressure-sensitive adhesives represent a preferred adhesive for use as aseparate layer. Examples of useful pressure-sensitive adhesives includepolyacrylate adhesives, natural rubber adhesives and thermoplasticrubber adhesives.

Polyacrylate adhesives comprise a polymer of an acrylate ester ofacrylic acid with a non-tertiary alcohol. These adhesives may alsocontain a minor amount of a copolymerized acid or amide. Adhesives ofthis type and methods for their preparation are known. See U.S. Pat. No.24,906.

The polyacrylate pressure-sensitive adhesives may be crosslinked ifdesired. Techniques for accomplishing this are known and described, forexample, in U.S. Pat. No. 2,925,174.

Useful natural rubber adhesives comprise natural rubber and, preferably,a tackifying resin. One such adhesive comprises natural pale creperubber (100 parts by weight), polyterpene resin (75 parts by weight),and antioxidant (1 part by weight). However, other useful natural rubberadhesives are also useful and will be apparent to those skilled in theart.

Useful thermoplastic rubbery adhesives comprise a rubbery blockcopolymer and, preferably, at least one resin compatible with the blockcopolymer. The rubbery copolymers have the general configuration A-B-Awherein the A units represent a thermoplastic polymer block with a T_(g)above 20° C. and the B units represent an elastomeric polymer blockformed from a conjugated diene. The A units are relatively incompatiblewith the B units and have an average molecular weight of from about5,000 to 125,000. Useful A units are styrene and useful B units arepolybutadiene or polyisoprene. An example of block copolymer of thistype is Shell Chemical Company Kraton 1101, a block copolymer of styreneand butadiene having one butadiene central block of 70,000 molecularweight and two terminal blocks of styrene of 15,000 molecular weighteach. Other block copolymers of this type may also be used.

Resins compatible with the block copolymer are known and include, forexample, hydrocarbon resins, coumarone-indene resins, dimerized rosins,metal resinates, hydrogenated rosins, poly-terpene resins and heattreated wood rosins. Still other resins are also useful and will beobvious to those skilled in the art.

The thickness of the adhesive layer is not critical to the presentinvention. Typically, the adhesive layer is from 10 to 50 microns thick.

Whether the article of the invention is inherently adhesive or uses aseparate adhesive layer, it preferably adheres over the entire range ofconditions normally encountered. Most preferably it exhibits a peeladhesion of at least 0.5 kg/cm width.

The article of the invention may be readily applied to a variety ofsubstrates. Preferably the article is positioned on the substrate suchthat the patterned surface will provide maximum drag reduction. When thepatterned surface comprises parallel peaks and valleys, maximum dragreduction is achieved when the peaks and valleys are generally parallelto the fluid flow. After being positioned, the article may be stretched,if necessary, to conform to the substrate surface and to remove unwantedwrinkles and air bubbles. The film is then adhesively secured to thesurface.

Several embodiments of the invention are shown in the drawings. FIG. 1illustrates an article of the invention comprising a sheet material 10having a patterned first surface 12.

Sheet material 10 may be inherently adhesive or, alternatively, it mayhave an adhesive second layer 14 applied to the surface of the sheetopposite patterned surface 12 as shown in FIG. 2.

In yet another embodiment, shown in FIG. 3, the sheet material 10comprises a carrier 16 and layer 18 bearing the patterned first surface12. Adhesive second layer 14 may be provided on the surface of carrier16 which is opposite the layer 18.

The patterned surface 12 shown in FIGS. 1-3 and 9 comprises a series ofparallel peaks 20 and valleys 22. The patterned surfaces 12 shown inFIGS. 1-3 have a symmetric, saw tooth cross section.

FIGS. 4-8 illustrate a number of alternative patterned surfaces that maybe used in the present invention.

In all of these embodiments, the patterned surfaces comprise a series ofessentially parallel valleys separated by a series of essentiallyparallel peaks. As can be seen from FIGS. 1-9, the cross section of thepatterned layer can have a variety of wave forms. For example, theembodiments of FIGS. 1, 2 and 3 have a symmetric saw tooth cross sectioncomprising peaks 20 and valleys 22. All of the peaks are identical asare all of the valleys.

FIG. 4 shows a series of parallel, symmetric, peaks 24 equally separatedby flat bottomed valleys 26.

FIG. 5 shows a series of alternating, parallel peaks 28 and 30 separatedby parallel valleys 22. Peaks 28 and 30 are parallel to one another butare of alternating heights.

FIG. 6 shows a pattern of repeating, parallel, symmetric, rounded peaks32. These peaks are separated by a series of parallel, symmetric valleys34.

FIG. 7 shows a series of parallel, symmetric, peaks 36 having concaveside walls. These peaks are separated from one another by a series ofparallel, round bottomed valleys 38.

FIG. 8 shows a saw-tooth pattern of alternating, parallel, assymetricpeaks 40 and assymetric valleys 42.

While only continuous peaks and valleys are shown, a discontinuouspattern of peaks and valleys is also contemplated in this invention.Thus, for example, the peaks and valleys may terminate for a portion ofthe article. The valleys may either narrow or widen as the peak orvalley progresses from one end of the article to the other. Stillfurther, the height and/or width of a given peak or valley may change asthe peak or valley progresses from one end of the article to the other.

The dimensions of the peaks and valleys are not critical to theinvention provided that whatever patterned surface is employed providesa reduction in drag. The optimum dimensions are somewhat dependent uponthe speed at which the substrate to be covered passes through the fluid.However, it has been found that peaks of from 20 to 400 microns high areuseful. Within this broad range it is preferred that the peaks be from20 to 150 microns high for high speed uses (e.g., aircraft) and from 120to 380 microns high for slow speed uses (e.g., automobiles).

The peak to peak spacing between adjacent peaks likewise is not criticalto the invention. It has been found that a spacing of from 20 to 400microns is useful. Preferably the spacing is from 20 to 150 microns forhigh speed uses and from 120 to 380 microns for slow speed uses.

The included angle between adjacent peaks can also vary within the scopeof this invention. For example, while flat and round bottom valleys areuseful, it is preferred that the valleys be generally V-shaped and havean included angle of from 15° to 140° (more) preferably from 50 to 60°).

The patterned surface 12 may be provided in-situ on the article of theinvention (see FIGS. 1 and 2) or it may be applied thereto as layer 18to carrier 16 (see FIG. 3). When layer 18 is employed to provide thepatterned surface, the same or different materials may be used as areused for carrier 16. When selecting different materials for use ascarrier 16 and layer 18 it is highly preferable that the two becompatible and either adhere together by themselves or be capable ofbeing adhered together tenaciously. It is also preferred that the twomaterials have similar degrees of conformability so that stress at theinterface between the two be minimized when the article is applied to asubstrate.

In constructions such as are shown in FIG. 3, the carrier is typicallyfrom 20 to 250 microns thick and the patterned layer is from 20 to 400microns thick.

The article of the invention may be prepared by several methods. Forexample, a sheet material may be extruded through a die capable offorming the patterned surface. Alternatively, the patterned surface maybe formed by embossing techniques utilizing heat and/or pressure. Othertechniques are also possible as will be understood by those in the art.

A specific useful embossing technique comprises extruding or casting asheet material and contacting the sheet while it is still hot with anengraved, chilled cylinder which bears the negative structure of thedesired patterned surface. The sheet may then be cooled on the cylinder.

Another useful technique comprises applying a radiation curablecomposition to a flexible carrier, contacting the radiation curablecomposition with a master bearing the negative structure of the desiredpattern, and radiation curing the composition. The resulting structuremay be removed from the master.

Yet another useful technique comprises preparing either an organosol ora plastisol composition, partially curing the composition (e.g., byapplying heat), applying the partially cured organosol or plastisol to aflexible carrier, contacting the organosol or plastisol surface to amaster bearing the negative structure of the desired pattern, and fullycuring the organosol or plastisol. Organosol or plastisol may also beused to provide a sheet material such as shown in FIG. 1.

While the foregoing description discusses coating techniques forapplying a patterned layer to a carrier, it is also possible to employlaminating techniques and/or adhesives to bond the two together.

Adhesive layers, when used, are applied to the surface of the articleopposite the patterned surface. A variety of techniques, such ascoating, spraying, or laminating, may be utilized to apply the adhesivelayer.

One useful method of applying the adhesive comprises contacting thesurface of the carrier opposite the patterned surface to an adhesivecarried on a release liner and passing the construction between rubberrolls. Either hot or cold lamination techniques can be employed.

The article of the invention may be provided as an opaque, translucentor transparent item. Graphic designs 44 may be incorporated into thearticle, see FIG. 9, preferably between the carrier and the patternedlayer. Alternatively, they may be placed on the patterned surface. Whenthe article of the invention is inherently adhesive, the graphic designs44 may be placed on either major surface.

The article of the invention may be made breathable by, for example,perforating it. While the shape and type of the perforations are not ofparticular importance it is preferred that they be such that anyadhesive used in the article does not flow together and seal theperforations. This can be achieved in many ways including, for example,by making the holes large enough to prevent such flow, and by deadeningthe adhesive around the walls of the perforations. Moreover, theperforations should not adversely affect the performance of the article,such as by causing it to separate from the substrate or by significantlyadversely affecting its drag reduction capability.

With these parameters in mind, it is preferred that the perforationshave a maximum dimension of less than 200 microns and preferably one inthe range of 10 to 100 microns.

Laser drilling may be used to provide the perforations in the article.It has been found that the perforations provided by this technique aregenerally conical in shape and have a generally circular cross section.The size of the opening on the surface first struck by the laser isgenerally wider than that of the opposite surface. The size and shape ofthe opening is, of course, dependent upon the type of laser employed,the power of the laser, and the time of exposure to the laser beam.

The present invention will be further described in the followingexamples wherein all "parts" are parts by weight unless otherwiseindicated. These examples are provided by way of illustration of theinvention and not by way of limitation.

EXAMPLE 1

A drag reduction article according to the invention comprising anextruded film was prepared. A patterned carrier was prepared from thefollowing ingredients:

    ______________________________________                                        COMPONENTS              PARTS                                                 ______________________________________                                        Polyvinyl chloride resin ("Diamond" 426                                                               100                                                   available from B. F. Goodrich)                                                Monomeric phthalate ("Santicizer" 711                                                                 15                                                    available from Monsanto)                                                      Monomeric phthalate ("Santicizer" 160                                                                 4                                                     available from Monsanto)                                                      Epoxy resin plasticizer ("Paraplex" G-62                                                              4                                                     available from Rohm and Haas)                                                 Barrium/Cadmium/Zinc ("Ferro" 5649                                                                    0.5                                                   available from Ferro Corp.)                                                   UV light absorber ("Mark" 1413                                                                        0.5                                                   available from Argus Chemical)                                                Phosphite stabilizer ("Ferro" 5227                                                                    0.5                                                   available from Ferro Corp.)                                                   Octadecanoic acid (available from Humko)                                                              0.4                                                   Inorganic silica ("Syloid" 244                                                                        1.0                                                   available from Davidson Chemical)                                             Violet dye ("Violet" ZIRS available                                                                   0.0073                                                from American Cyanamid)                                                       ______________________________________                                    

The ingredients were mixed together and charged to a 30:1length:diameter single screw (6.4 cm. diameter) extruder having a diewith an 85 cm wide ×0.7 cm high opening. The extruder screw had fivezones maintained at, respectively, 170° C., 172° C., 174° C., 176° C.,and 180° C. The hot extruded film was cast onto an engraved chilledcylinder. The cooled film replicated the groove pattern of the cylinder.The film was 76.3 cm wide by 0.05 cm thick and had a cross section ofthe type shown in FIG. 2. The patterned first surface comprised a seriesof parallel, triangularly shaped ridges extending along the longitudinalaxis of the film. The height of the ridges was 300 microns, thepeak-to-peak spacing between adjacent ridges was 500 microns, and theincluded angle between adjacent ridges was 53° .

A pressure sensitive adhesive was prepared as described in U.S. Pat. No.24,906 using a blend of 90 parts by weight 2-methyl butyl acrylate and10 parts by weight acrylic acid.

The adhesive was applied to a silicone liner (SCW 106 from the GeneralElectric Company) using a notched bar to a wet thickness of 125 micronsat a coating speed of 51 meters/minute (m/min) and then dried in aforced air oven having four heated zones maintained respectively at 54°C., 65° C., 77° C. and 87° C. The adhesive was then laminated at roomtemperature to the second surface of the patterned carrier.

The resultant film was tested by removing the release liner and applyingit to a curved surface. The film conformed exactly to the surface. Theedges of the film did not curl away from the surface after application.

A portion of the film was applied to a flat metal plate and tested fordrag reduction. The film provided a reduction in drag of 5% compared tothe drag across a smooth flat metal plate.

EXAMPLE 2

A drag reduction article according to the invention comprising aseparate patterned surface layer was prepared.

A cast vinyl carrier film was prepared from the formulation used inExample 1 to prepare the patterned carrier. The vinyl resin was appliedto a removable paper liner (SCW 174 available from the General ElectricCompany) at a rate of 390 meters/minute. The vinyl resin was dried andfused in a five zone oven. The zones were maintained respectively at 46°C., 57° C., 143° C., 174° C., and 210° C. The film was cooled to providea film which was 76.3 cm wide by 100 microns thick and the linerremoved.

A plastisol coating was prepared from the following composition:

    ______________________________________                                        COMPONENTS             PARTS                                                  ______________________________________                                        Polyvinyl chloride resin ("Geon" 128                                                                 54.6                                                   available from B. F. Goodrich)                                                Diisodecyl phthalate (available                                                                      43.7                                                   from Monsanto Chemical)                                                       Cadmium/Zinc ("Nuostab" 1923                                                                         1.7                                                    available from Nuodex Tenneco)                                                ______________________________________                                    

The plastisol coating was applied to a 40 cm width of a first surface ofthe carrier using a notched bar. The coated film was then dried at 37°C., embossed with an engraved cylinder using heat and pressure and thenpassed through a forced air oven at a rate of 3 meters/minute to fusethe plastisol. The oven had three zones maintained respectively at 37°C., 143° C., and 165° C. The resulting patterned surface had the crosssection shown in FIG. 2 wherein the patterned surface layer was 300microns high; the peak-to-peak spacing between adjacent ridges was 500microns; and the included angle was 53° .

A pressure sensitive adhesive was applied to the surface of the vinylcarrier opposite the patterned surface using the formulation andtechniques described in Example 1. When applied to a metal plate, thefilm conformed exactly to the plate and provided a 5% reduction in dragacross the plate.

EXAMPLE 3

A drag reduction article according to the invention comprising aseparate patterned layer was prepared which employed a cast vinyl film(prepared using the ingredients and techniques described in Example 2)and an organosol composition. The organosol composition was preparedfrom the following ingredients:

    ______________________________________                                        COMPONENTS             PARTS                                                  ______________________________________                                        σ- & m- Xylene   12.42                                                  Diisobutyl Ketone      9.4                                                    Mineral Spirits        5.5                                                    Plasticizer ("Admex" 770 available                                                                   16.4                                                   from Sherex Corp.)                                                            Cadmium/Zinc ("Nuostab" V1923                                                                        2.2                                                    available from Nuodex Tenneco)                                                Substituted acrylonitrile                                                                            2.2                                                    ("Uvinul" N-539 available                                                     from Ciba Geigy)                                                              Polyvinyl chloride resin ("Geon" 178                                                                 44.4                                                   available from B. F. Goodrich)                                                Acrylic copolymer ("Elvacite" 2013                                                                   7.3                                                    Solution available from DuPont)                                               ______________________________________                                    

The coating was applied to a first surface of the carrier using anotched bar. The coating was then dried at 126° C., embossed with anengraved cylinder using heat and pressure, and fused in a forced airoven having two zones maintained respectively at 20° C. and 170° C.

The resulting patterned surface had a cross section of the type shown inFIG. 2 wherein the patterned surface layer was 80 microns high; thepeak-to-peak distance between adjacent ridges was 200 microns; and theincluded angle was 53°.

A pressure sensitive adhesive was applied to the surface of the carrieropposite to the patterned surface using the formulation and thetechniques described in Example 1. When applied to a metal plate, thefilm conformed exactly to the plate and provided a 5% reduction in dragacross the plate.

EXAMPLE 4

A drag reduction film according to the invention was prepared bypreparing a vinyl carrier from the vinyl composition of Example 1. Thevinyl composition was coated onto a 75 micron thick polyester liner to awet thickness of 100 microns and then passed through a forced air ovento dry it. The oven had five zones maintained respectively at 43° C.,99° C., 143° C., 149° C. and 182° C.

A radiation curable composition having the following ingredients wasroll coated onto the vinyl film to a thickness of 300 microns.

    ______________________________________                                        COMPONENTS             PARTS                                                  ______________________________________                                        Urethane acrylate oligomer ("XP51"-85                                                                67.9                                                   available from Cargile)                                                       Tetraethylene glycol diacrylate                                                                      19.2                                                   ("SR"-268 available from                                                      Sartomer Company)                                                             Diethoxyacetophenone ("DEAP"                                                                         4.8                                                    available from Upjohn)                                                        Fluorochemical surfactant ("FC"-431                                                                  2.7                                                    available from Minnesota Mining                                               and Manufacturing Company)                                                    N-vinyl pyrrolidone    4.9                                                    (available from GAF)                                                          UV light stabilizer ("Tinuvin" 770                                                                   0.5                                                    available from Ciba Geigy)                                                    ______________________________________                                    

The resulting construction was then laminated to an engraved surfaceusing a laminator pressure of 3 kg/cm² and a laminator speed of 9meters/minute.

The radiation curable composition was exposed through the polyester andcarrier to ultraviolet light in a Linde UV Processor from Union CarbideCorporation to cure it. Exposure conditions were:

Processor length: 2.4 meters

Processor speed: 9 meters/min.

UV Exposure level: 2 passes at 1.45 J/cm² ea.

Processor N₂ level: 220 ft³ /hr. - ft. width.

The resulting construction was removed from the engraved surfacerevealing a patterned surface having a cross section similar to that ofFIG. 2. The thickness of the patterned surface layer was 33 microns; thepeak-to-peak distance between adjacent ridges was 33 microns; and theincluded angle was 53° . The polyester liner was then removed and apressure sensitive adhesive laminated to the side of the carrieropposite the patterned surface using the materials and techniquesdescribed in Example 1.

The film was applied to a flow control surface on an airplane. The filmconformed exactly to the surface and provided a 6.5% reduction in dragacross the surface.

EXAMPLE 5

A drag reduction film was prepared. The radiation curable composition ofExample 4 was applied to a polyester film and cured as described inExample 4 to provide a grooved liner. The grooved surface of the linerwas treated with a release coating and a polyurethane composition havingthe following ingredients was applied to the patterned surface of theliner.

    ______________________________________                                        COMPONENT                PARTS                                                ______________________________________                                        Polyester polyol (available from                                                                       65.9                                                 Mobay Chemical as "Desmophen" 670)                                            0.1 Second cellulose butyrate                                                                          2.4                                                  (available from Eastman Chemical as                                           "CAB" 381-0.1)                                                                Methyl isobutyl ketone   10.9                                                 Polyglycol ether ester (Cellosolve                                                                     16.8                                                 acetate available from Dow Chemical Co.)                                      UV Stabilizer ("Irganox" 1010                                                                          1                                                    available from Ciba Geigy)                                                    UV Stabilizer ("Tinuvin" 328                                                                           1                                                    available from Ciba Geigy)                                                    UV Stabilizer ("Tinuvin" 770                                                                           2                                                    available from Ciba Geigy)                                                    Aliphatic isocyanate (Aliphatic                                                                        36.3                                                 isocyanate available from Mobay                                               Chemical as "Desmodur" N-100)                                                 Dibutyl Tin Dilaurate    0.4                                                  (1% by weight in Xylene)                                                      ______________________________________                                    

The polyurethane composition was cured to a tack free film bysequentially heating it to 65° C. for one minute, 107° C. for oneminute, and 121° C. for one minute, and 163° C. for one minute. Thepolyurethane was then fully cured by exposing it to room temperature for7 days. The film was then stripped from the patterned liner and apressure sensitive adhesive applied as described in Example 1. Theresulting drag reduction film could be applied to and conform tocompound surfaces to reduce drag thereacross.

We claim:
 1. An article having reduced drag resistance to a fluidflowing thereover, said article comprising a conformable, crosslinkedsheet material having a patterned first surface which contacts saidfluid and which reduces said drag resistance, wherein said patternedsurface comprises a series of parallel peaks separated from one anotherby a series of parallel valleys.
 2. An article according to claim 1wherein said polymeric sheet is made from a material that demonstratesno change after being placed in TT-S-735 hydrocarbon fluid for 72 hoursaccording to test method BMS-10-30A.
 3. An article according to claim 1wherein said crosslinked polymeric sheet comprises a thermoset polymer.4. An article according to claim 1 which shows no change after beingsubjected to the flexibility test of MIL-P-38477A.